Gradient Li-rich oxide cathode particles immunized against oxygen release by a molten salt treatment

Abstract

Lithium-rich transition metal oxide (Li1+XM1−XO2) cathodes have high energy density above 900 Wh kg−1 due to hybrid anion- and cation-redox (HACR) contributions, but critical issues such as oxygen release and voltage decay during cycling have prevented their application for years. Here we show that a molten molybdate-assisted LiO extraction at 700 °C creates lattice-coherent but depth (r)-dependent Li1+X(r)M1−X(r)O2 particles with a Li-rich (X ≈ 0.2) interior, a Li-poor (X ≈ −0.05) surface and a continuous gradient in between. The gradient Li-rich single crystals eliminate the oxygen release to the electrolyte and, importantly, still allow stable oxygen redox contributions within. Both the metal valence states and the crystal structure are well maintained during cycling. The gradient HACR cathode displays a specific density of 843 Wh kg−1 after 200 cycles at 0.2C and 808 Wh kg−1 after 100 cycles at 1C, with very little oxygen release and consumption of electrolyte. This high-temperature immunization treatment can be generalized to leach other elements to avoid unexpected surface reactions in batteries.

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Fig. 1: Redox behaviour and structural design of Li1+X(r)M1−X(r)O2 particles with a continuous gradient from the Li-rich bulk to the Li-poor surface.
Fig. 2: Characterizations of Li1+X(r)M1−X(r)O2 single crystals and quantification of X(r).
Fig. 3: Electrochemical behaviours of the pristine Li1.20Mn0.48Co0.16Ni0.16O2 and Li1+X(r)M1−X(r)O2.
Fig. 4: Valence profiles of oxygen and M in gradient LX(r)MO in the charge process.
Fig. 5: Mn oxidation states and structural damage after cycling.
Fig. 6: Stabilization of Li diffusivity and full-cell cycling.

Data availability

The data that support the plots in this paper and other findings of this study are available from the corresponding author upon reasonable request.

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Acknowledgements

We acknowledge the support from NSF ECCS-1610806 and Wuxi Weifu High-Technology Group Co., Ltd. This research used resources of the Center for Functional Nanomaterials and the 23-ID-2 (IOS) beamline of the National Synchrotron Light Source II, both of which are US Department of Energy Office of Science user facilities at Brookhaven National Laboratory, under contract DE-SC0012704. Also, this work was performed in part at the Center for Nanoscale Systems, a member of the National Nanotechnology Coordinated Infrastructure Network supported by the National Science Foundation under NSF award no. 1541959.

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Z.Z. and J.Li conceived and designed the experiments. Z.Z. synthesized the materials and performed the electrochemical tests. D.Y, Y.Y. and B.W. performed the HRTEM imaging, STEM-EDS mapping, EELS line scan and focused ion beam sample preparation for aberration-corrected STEM characterizations. C.S. took aberration-corrected STEM images and performed the DFT calculations. D.Y., I.W. and A.H. measured the soft X-ray absorption. Z.Z., D.Y. and X.Y. did the sXAS data analysis. Z.Z. and J.Li wrote the paper. All authors analysed the data, discussed the results and commented on the manuscript.

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Correspondence to Ju Li.

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Supplementary Information

Supplementary Figs. 1–14, Tables 1–3, Note 1, Discussion 1–4 and refs. 1–8.

Supplementary Video 1

M and O redox behaviours in the charging process.

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Zhu, Z., Yu, D., Yang, Y. et al. Gradient Li-rich oxide cathode particles immunized against oxygen release by a molten salt treatment. Nat Energy 4, 1049–1058 (2019). https://doi.org/10.1038/s41560-019-0508-x

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